Polyphase transformer arrangement



Oct. 18, 1949. A s c ND, JR 2,484,866

POLYPHASE TRANSFORMER ARRANGEMENT Original Filed Jan. 25, 1944 i 2 3 7i3 I H b i n o o 0 a C i9 3 9 S H 4 76 I N VEN TOR HAROLD A, STRICKLAND3.

TTORNP Patented Oct. 18,

2,484,866 POLYPHASE TRANSFORMER ARRANGEMENT HaroldA. Strickland, J r.,Detroit, Mich., assignor, by mesne assignments, to The Ohio Crankshaftggilnpany, Cleveland, Ohio, a corporation of Original applicationJanuary 25, 1944, Serial No.

Divided and this application November 18, 1946, Serial No. 710,463

4 Claims. 1

This invention relates to polyphase transformer systems and thisapplication is a division of my copending application, Serial No.519,637, filed January 25, 1944, now Patent No. 2,440,309, dated April27, 1948.

An object of the invention is the provision of circuit means, includingtransformers, for reducing the number of transformers necessary in thetransformation of polyphase current from commercial line sources to adistributing circuit without a reduction in the transferred power.

Other objects pertain to simplicity of arrangement, decrease in weight,with maintenance of efficiency in a polyphase system of transformation.

In the single single figure of the drawing there is showndiagrammatically a circuit indicating the mesh arrangement connectingthe power source to the distributing circuit. An actual application ofthis circuit in induction heating apparatus is shown in my abovereferred to copending patent, which application should be consideredpurely from the standpoint of illustrating one embodiment of anapplication and not as limiting the invention described herein to anyone specific application.

In this figure numerals I, 2 and 3 designate lead-in conductors of athree-phase commercial power system, the voltage value betweenconductors being assumed for illustrative purposes as 460 volts in adelta connection indicated at 4, a common power arrangement inindustrial plants. The delta terminals are designated a, b and c. Inorder to provide a common return connection for the load 5 with theswitch-containing conductors of the three-phase distributing circuit, aY-connection is made to the delta mesh with the neutral point at a andend points 0, x, 11, there being a transformer connection in deltabranches a--b and bc only, to form the two Y-arms a,:u, 41-11:, thethird arm being delta branch ac. Capacitors are connected between pointsa-c, a:r and a11 of the delta mesh. The capacitors mentioned serve as ahigh-frequency by-pass but are not essential for the effective operationof the transformation.

With the arrangement shown the phase voltage between adjoiningY-conductors is increased over the delta phase voltage alone. Thisvoltage is effective across the load capacitor 6, as shown in thediagram, the capacitor having a series connection to the load 5. Theroot mean square voltage available for the load circuit is only 460volts, butif the delta circuit is used with a superimposed Y, asindicated by the adJoining diagram the voltage from the neutral to thedelta Junction would be 460/V3. It is, therefore, to get 460 volts and acommon phase point that the circuit as described is used. It is, ofcourse, possible to use a conventional transformation, but to do sorequires approximately 50% more kilovolt amperes of transformer withproportionately more space required and additional cost.

In utilizing the transformer arrangement as described, one arrangementis shown in the figure wherein opposed rectifying elements I and 8, 9and I0, and II and I2 are placed in the distributing conductors I 3, I4and I5 leading from the transformer points 11, a: and 0, respectively.Each group of rectifiers consists of two opposed elements, as, forexample, in the Y-circuit rectifier, 7 allowing current conduction inone direction and 8 in the other. As shown in my c0- pending patent, therectifying elements may be of the type wherein the commencement of theconduction in one direction may be readily con trolled. The threeconductors I3, I4 and I5 have a common connection at I5 through thecommon return I! to the neutral point a of the Y-mesh, this conductorincluding the capacitor 8 and the load 5. Capacitors I8, I9 and 20between the transformer points a1 a--:c and ac are useful to by-passhigh-frequency currents. Preferably the capacitance of each of thesecapacitors should substantially exceed that of the load capacitor 6, avalue of four times being found effective. With this arrangement it ispossible to transform the polyphase incoming current alternately to eachof the three conductors I3, I4 and I5 and secure a current flow throughthe common return and load 5 in a series of intermittent power pulses.As shown in my above referred to copending patent, alternate powerpulses through the load 5 and capacitor 6 are in opposite directions.Thus, one power pulse tends to charge the capacitor through the loadpositive, while the next succeeding power pulse tends to discharge thecapacitor through the load in the negative direction and to then chargeit negatively. As the alternate discharges and charges occur, anoscillatory condition is set up in the capacitor 6 and the load coil 5,thereby producing the high-frequency current in the load 3 coil 5 whichmay be induced into workpieces suitably coupled electrically thereto.

It is pointed out that the transformer ratio is 1 to 1, thus permittinga direct connection to the distributing circuit at conductor I! from thesource conductor 3.

Obviously other types of loads may be em-' electrically related to eachbranch of said delta mesh, a load including an inductance andcapacitance in series relationship, and connections from said neutralpoint and the free ends of said Y-network to said load.

2. An electrical power translating circuit comprising three terminals,each terminal being connected to one phase of a three-phase powersource, a, delta mesh including said terminals, a Y-network havingconnection to one of said terminals as a neutral point and havingbranches electrically related to each branch of said delta mesh, two ofsaid branch relationships being inductive and all three branchesincluding a capacitor connected in parallel, a load including aninductance and capacitance in series relationship litor, and atranslating network between said source and load comprising a delta meshconnection between said terminals, two branches of which each includes aprimary or a transformer, and the third of which is transformer-free, aY- network connected to said delta mesh comprising three branches eachconnected at one end to one end of the transformer-tree branch of saiddelta mesh to iorm a neutral point, one branch of said Y-networkincluding the transformer-free delta branch, and each 0! the otherY-network branches including a secondary oi said delta meshtransformers, said load circuit being connected between said neutralpoint and the free ends 01' the Y-branches.

4. An electrical power supply system comprising a three-phase powersource having three terminals, a load circuit including an inductor andcapacitor, and a translating network between said source and loadcomprising a delta mesh connection between said terminals, two branchesof which each includes a primary of a transformer and the other of whichis transformerfree, a Y-network connected to said delta mesh comprisingthree branches each connected at one end to one end of thetransformer-free branch of said delta mesh to form a neutral point, onebranch of said Y-networlr including the transformer-tree delta branchand each of the other Y-network branches including a secondary of one ofsaid delta mesh transformers having a 1 to 1 turn ratio to the primarythereof, said load circuit being connected between said neutral pointand the free ends of the Y-branches.

HAROLD A. STRICKLAND, Ja.

No references cited.

